A High-Efficiency Wideband Grating Coupler Based on Si₃N₄ and a Silicon-on-Insulator Heterogeneous Integration...

To fully utilize the advantages of Si₃N₄ and Silicon-On-Insulator to achieve a high-efficiency wideband grating coupler, we propose and numerically demonstrate a grating coupler based on Si₃N₄ and a Silicon-On-Insulator heterogeneous integration platform. A two-dimensional model of the coupler was established and a comprehensive finite difference time domain analysis was conducted. Focusing on coupling efficiency as a primary metric, we examined the impact of factors such as grating period, filling factor, etching depth, and the thicknesses of the SiO₂ upper cladding, Si₃N₄, silicon waveguide, and SiO₂ buried oxide layers. The calculations yielded an optimized grating coupler with a coupling efficiency of 81.8% (-0.87 dB) at 1550 nm and a 1-dB bandwidth of 540 nm. The grating can be obtained through a single etching step with a low fabrication complexity. Furthermore, the fabrication tolerances of the grating period and etching depth were studied systematically, and the results indicated a high fabrication tolerance. These findings can offer theoretical and parameter guidance for the design and optimization of high-efficiency and broad-bandwidth grating couplers.